Electromagnetic coupling device or electrical transformer



Nov, 8, 1932. F. w. TWORT 1,887,470

ELECTROMAGNETIC COUPLING DEVICE OR ELECTRICAL TRANSFORMER Filed Sept. 27, 1928 YCCLBHCK W Wort ATTORNEYS Patented Nov. 8, 1932 .EY, ENGLAND ELECTROMAGNETIC COUPLING OR ELECTRICAL TRANSFORMER Application filed September 2'7, 1928, Serial No.

This invention relates to electro-magnetic coupling devices or electrical transformers by means of which two electrical circuits may be electro-magnetically coupled together. Although the invention is particularly applicable to the coupling of two circuits tuned to very high radio frequencies, such as are employed in radio signalling upon short wave lengths, it is applicable to the coupling of circuits of any frequencies, and in fact has distinct advantages in connection with operation upon longer wave lengths.

The main object of the present invention is to provide a device in which energy can be transferred from one winding to another without any appreciable dissipation of en ergy and without any of the energy being taken by components in the electrical circuits oth r than the winding which it is re sired to influence. The invention also aims at arranging two or more windings so that at any given point desired relative oscillatory potentials may be obtained, and to enable this to be carried out without affecting the coupling between two windings. The invention provides windings which exhibit extraordinar stability and. low losses, while being particularly insensitive to outside disturbances such as those commonly experienced due to the body capacity of the ope"- ator. The novel coils are thus extraordinarily selective and have very low self-cm pacity so that for any given frequency or wave length, a maximum value of inductance can be employed.

According to the present invention, a coupling device having two or more windings is arranged with one winding so placed relatively to another that each of its conductors is substantially shielded from its neighbouring conductors in such a way as to prevent the alternating fields set up by the current flowing in each conductor of the shielded winding from having access to any other con-- ducting body than the corresponding conductor of the other winding with which it is coupled. The most satisfactory arrangement is to wind the conductors so that those of one of the windings substantially encir cle or embrace the conductors of the other 308,844, and in Great Britain October 4, 1327.

winding; for example, by enclosing the latter conductors within the former conductors, which may be formed of metal tubes. Each conductor of a secondary winding may encircle a conductor of primary winding, although if there is a step-up or step-down effect to be obtained, naturally the number of turns in the two windings will not be the same.

It is found in practice that the complete shielding of one winding by the other, turn by turn, is of most importance when operating on extremely high frequencies, that is to say, for short wave length radio reception, and, on the other hand, the feature of the balance winding that is to say with each winding arranger with half on one side and the other half on the other side of the ends of the windings and with the winding coupled wih it having those of its turns associated wi a turns of the first-mentioned winding disposed symmetrically on either side of the terminal ends of the windings, is of most importance on higher wave lengths, and in particular when working on the so-called broadcast band, or more particularly, approximately between 250 metres and 600 metres. It may be mentioned that in working with the novel device on wave lengths below 50 metres, the losses are reduced to a very considerable extent in comparison with those previous coupling devices and that successful high frequency amplification can be obtained to an extent which it is believed has been hitherto impossible.

In order that the invention may be clearly understood and readily carried into effect, one particular form of the novel coupling device will be described with reference to the accompanying drawing, in which Figure l is a s de elevation of one example 0* )ling device in accordance with the s is a plan view of Figure 1, and higure 3 1s a section through one side of coupling device on the line VV in Fig ure 2; it is on an enlarged scale and shows clearly the disposition of the primary and secondary conductors;

Figure e 18 a diagrammatic illustration of the coupler for the purpose of indicating the internal connections, while Figure 5 shows a conventional circuit arrangement illustrating how the coupling device could be employed in a two-stage hi h frequency amplifier for short waves.

Referring first of all to Figures 1 to 4 of the drawing, the windings of the coupler are wound on a tubuler former a of insulating material substantially cylindrical in shape with spaced peripheral ribs Z2 notched to receive the windings. The secondary winding comprises two halves 0 0 consisting of relatively line copper tube. The primary winding is a fine cotton-covered copper wire and it is not visible except i Figure 3 as it lies inside the tubular secondary winding, but will be described below with reference to its path and the secondary conductors through which it is threaded.

The actual disposition of the windings will be best seen in Figure 4-. One end of the secondary winding is connected to a contact member IS. The winding then proceeds around the former, making five and a halt turns constituting the upper half 0 After arriving at the top turn, it proceeds by an internal conductor (Z to a further contact member 5T which is conveniently arranged so that it can be connected by a conductor to the neXt contact member ST? The contact member {5T is joined to the lower half 0 of the secondary winding, which constitutes iive and a halt turns, finally ending at the contact member OS. These contact members are shown diagrammatically placed in Figure their true position is indicated in Figure 2 where they are lettered correspondingly. The two remaining contact members IP and OP are the beginning and ending terminals of the primary winding. The connections of this winding are clear in Figure 4, and the actual disposition of the contact members is clearly seen in Figure 2. By the arrangement of the contact members in pairs diametrically opposite,'no connection leading to damage can be made when the device is plugged into a suitable base or holder such as a hollow piece of insulating material or" the same shape as the former a and having a number or" spring contacts around its upper edge to receive the projecting terminals on the coupling member.

It will be noted that the primary winding consists of cotton-covered wire threaded through the turns of the tubular secondary windings 0 0 It consists of two and a hall"- turns, one anda quarter turns lying in the uppermost two turns 01 the secondary winding 0 and the other one and a quarter turns lying in the lowermost two turns of the sec-- tion 0 of the secondary winding, while the two portions are connected together by the conductors 70 The uppermost turns are seen at 76 in Figure 3.

It will therefore be noted that the actual beginning and ending terminal of the secondary winding are in the middle so to speak, that is to say, they actually come out of the former between the upper turns 0 and the lower turns 0 and are merely brought down to the contact members and OS by conducting wires. Similarly, the primary turns are divided into two halves which are symmetrical with regard to the centre of the secondary winding. T he actual mid-point of the secondary winding is represented by the conductor (Z which joins the upper turn of t is section 0- to the contact member ST the latter being connected by an external wire on the base of the device to th contact member ST which is in turn connected to the lower turn of the section 0 When a tapis required from the mid-point oi the secondary coil, it is taken from one of the contact members $31 and ST? Figure 5 illustrates a simple two-stage frequency ampl'ner particularly infor short wave reception. It consists o alves Z and Z the former coupled to the aerial m by a coupling device a constructed in accordance with the invention, and the second valve Z is coupled to the first valve Z by a second coupling device a constructed in accordance with the invention. In each case the mid-point of the secondary windings is connected through a high resistance 0 or 0 to the filament of the respective valve. This midpoint, of course, is in fact the conductor (Z, and the fact that this is connected to the valve filaments is found to give a very stable result, the winding being hardiy sensitive at all to body capacity due to the approach of the operations hand and so forth. The lower ends of the secondarywindings are joined by neutralizing condensers p and p to the anodes of the respective valves in quite the usual fashion.

It will be realized that th invention is not limited to the use oi tubular conductors for the encircling winding, as the same cdect may be substantially obtained by using strip or tape and wrapping this round, folding it over, or winding it helically around the conductors of the inner winding so that tl e latter are substantially enclosed in the strip or tape. Again, instead oi encircling some turns of the primary winding by some turns of the secondary winding, the primary winding may be made tubular and the secondary windhave its turns located within those of the primary winding. It will be understood that the conductors of the tubular winding may be made of any suitable metal and that the conductors of the inner winding may be covered with any suitable insulating material, or alternatively that tube of insulating material may be inserted in the tubular conductors.

The benefits of the invention can be obtained in a device having more than two windings. To give an example of this, a coupler may be made according to the invention embodying a reaction coil as well as the primary and secondary windings of the cou pler. The primary turns may then pass through some of the turns of the secondary winding and the turns of the reaction coil pass through other turns of the secondary winning, or again, the reaction coil may be distinct from either the primary or secondary windings. Again, more than two coils may be arranged concentrically, for example the primary winding may also be hollow and may contain another winding forming part of the electrical circuit so as to influence it.

Having thus described my invention what I claim as new, and desire to secure by Letters Patent is 1. An electro-magnetic coupling device comprising a substantially cylindrical former of insulating material, a tubular secondary winding wound helically upon said former in two halves, the terminal points of said winding being free ends of the two adjacent or central turns, and a primary winding of fewer turns than said secondary winding and disposed symmetrically within the outermost pairs of turns of said secondary winding.

2. A radio frequency coupling device co1nprising two windings, certain turns of one of said windings being substantially tubular and each substantially enclosing one turn of the other winding within its tubular structure, the windings having their terminal ends at which current enters and leaves disposed adjacent the longitudinal centre of each winding.

3. Electromagnetic coupling device 00m rising a substantially cylindrical former of insulating material, a tubular secondary winding wound helically upon said former in two halves, the terminal point of said winding being free ends of the two adjacent or central turns, and a primary winding of fewer turns than said secondary winding and disposed within atleast one of the turns of said secondary winding.

4. A radio frequency coupling device comprising two windings, certain turns of one of said windings each substantially inductively shielding individual turns of the other winding, the turns of the windings being so disposed that their terminal ends at which current enters and leaves are disposed adjacent the longitudinal centre of each winding.

In witness whereof I hereunto subscribe my name this 17th day of September, A. D. 1928.

FREDERICK WILLIAM TWVORT. 

